Conventionally, to form a surface protective film and an interlayer insulating film of semiconductor devices, polyimide resin or polybenzoxazole resin is widely used that has all of excellent heat resistance, electrical properties, mechanical properties, and the like. These resins are less soluble in various solvents and therefore generally used as a composition prepared by dissolving a precursor of the resins in a solvent. Accordingly, a step of cyclizing the precursor is necessary when used. The cyclization step is carried out by thermal curing for heating the precursor to usually 300° C. or higher.
In recent years, however, semiconductor devices less heat-resistant than conventional ones have been developed, and there is thus a desire to lower thermal curing temperatures for a surface protective film material or an interlayer insulating film material. Particularly, thermal curability at 250° C. or lower is often desired.
In order to satisfy such a desire, Patent Literature 1 and 2 below each propose a material that does not need the cyclization step and is excellent in cost performance and photosensitivity, which is prepared by using a phenolic resin obtained from the condensation of phenols and aldehydes widely used as base resins in the field of resists, and crosslinkable microparticles or a core-shell polymer, which can be added to improve thermal shock resistance of the phenolic resin.
Additionally, in Patent Literature 3 below, upon synthesis of a phenolic resin, to improve the thermal shock resistance of the phenolic resin, at least one substituted xylene compound selected from the group consisting of an α,α′-dihaloxylene compound, an α,α′-dihydroxyxylene compound, and an α,α′-dialkoxyxylene compound is used instead of an aldehyde compound. Patent Literature 3 proposes a material obtained from the condensation of the substituted xylene compound and a phenolic compound.
Furthermore, Patent Literature 4 below describes a material prepared by using both of a phenolic resin having a condensation product of a biphenyl compound with a phenol in a skeleton thereof, and a photo acid-generating agent. However, in Patent Literature 4, the material is disclosed as one for forming a liquid crystal alignment control protrusion and/or a spacer, or as one for forming a liquid crystal alignment control protrusion and a spacer simultaneously.
However, even if any of these materials is applied to a semiconductor device, as a surface protective film or an interlayer insulating film, the reliability thereof is low. Therefore, it has been difficult to use the materials as alternatives to polyimide resin and polybenzoxazole resin.